View Compilation Error

0_0_15989541_7223.cpp: In function 'void init()':
0_0_15989541_7223.cpp:9:17: error: 'd' was not declared in this scope
         dp[i] = d[i - 1] + 4 * (i - 1) + 2 - 1; //第n条折线应该与前n-1条折线的两条边都相交时交点最多，此时有4*(n-1)条线段和两条射线，但是端点处两条线段相交，故要减去1
                 ^